A sadistic thug broke into a wildlife centre and beheaded a wallaby, making off with its head.
Police are now hunting whoever carried out the horrific attack at the Brent Lodge Animal Park in Hanwell, in west London.
The killing happened some time on Wednesday evening after someone broke into the centre.
Officers from Scotland Yard say Bruce was beheaded with a knife by an intruder who had earlier cut through a perimeter fence to enter the enclosure.
Shocked staff later discovered the animal's corpse in its enclosure with its head missing.
A lack of CCTV has hampered inquiries into the killing.
A member of staff at the centre said that Bruce's head hadn't been found, but was too upset to say if it could have been taken as a sick trophy.
Police are yet to make any arrests, and are unsure whether the wallaby was killed by a single person or a group.
A Scotland Yard spokesman said: 'We were alerted on Thursday morning when staff went in and found the horrific sight.
'At some point during the evening of Wednesday someone gained entry to the Brent Lodge Animal Park by cutting through the fence and, once inside, killed the animal.'

Seven-year-old Bruce is a Parma wallaby who had only moved to the park from a zoo in Norfolk six months.
No other animals were injured in the attack, but the park’s other wallaby, Rolph, was 'in a visibly distressed state,' an Ealing Council spokeswoman said.
Detective Inspector Tim Yates, from Ealing CID said: 'I know the families who use this park will be very concerned about this attack, but it is a very unusual incident and we are determined to find those responsible'.
The park is home to small animals such as goats, peacocks rabbits and wallabies.
Councillor Bassam Mahfouz, Ealing council's cabinet member for environment said: 'I’m completely sickened by this attack on a defenceless animal and I know the whole community will be equally shocked.
'We will give police every assistance with their enquiries to find the person responsible and I would appeal for anyone with any information to come forward'.
No arrests have been made and enquiries are ongoing.